Mucoid enteritis is a fatal disease of rabbits with excessive mucus secretion into the gastrointestinal tract. Available evidence suggests the infectious nature of this disease. However, the etiology of this disease remains unknown. In our laboratory, the haemophilus-like microorganism was isolated from the gastrointestinal tract of rabbits with mucoid enteritis. The results of the preliminary study suggest that this microorganism causes mucoid enteritis in rabbits. In this project, the pathogenicity of previously isolated haemophilus-like microorganism in rabbits will be investigated. Various routes and doses of the microorganism will be tested in developing mucoid enteritis in experimental rabbits. This project will include the study on the susceptibility of various breeds, ages, and sexes of the rabbits to the haemophilus-like infection. The influence of the various stressful conditions on the susceptibility of the rabbits to the haemophilus-like microorganism infection will also be studied. Furthermore, the mechanism of the developing mucoid enteritis in rabbits infected with this microorganism will be investigated. Subsequently, the incidence of the haemophilus-like infection in rabbitries and its relationship to the incidence of mucoid enteritis will be determined. The incidence of infection in a large population of rabbits will be investigated by detecting a specific antibody to the haemophilus-like microorganism in the sera from rabbits. The comparative study on the prophilaxis and therapy in haemophilus-like infection and in spontaneous mucoid enteritis in rabbits will also be included in this project. The results of this study will be decisive in determining whether or not the haemophilus-like microorganism is the etiological agent causing mucoid enteritis. These results will also provide information on experimental reproductibility of mucoid enteritis with haemophilus-like microorganism. The similarity between the mucoid enteritis and cystic fibrosis has been suggested by several investigators with particular reference to the chronic and excessive discharge of mucus. Thus the data obtained from this study may be of significance in establishing mucoid enteritis in rabbits as an animal model for studying cystic fibrosis in man.